Nondestructive Determination of Relative Plutonium Content in MOX Fuel Pins for Pressurized Heavy Water Reactors Using Passive Gamma Scanning

Passive gamma scanning (PGS) for detecting the variations in relative PuO₂ content (composition) in (U,Pu) mixed oxide (MOX) fuel pins with low PuO₂ content (0.4%) for pressurized heavy water reactors is demonstrated. Experiments are carried out with MOX pins of varying compositions with a NaI(Tl) detector. An annular detector was used to improve the counting statistics, and it was demonstrated that a change of PuO₂ content of ±0.02% could be detected at a very low level of PuO₂ content of 0.4%. It was also observed that a larger-sized PuO₂ agglomerate of 1 mm located near the surface of the pellets could be detected during PGS of the welded fuel pins.